Integrated circuit (IC) packages must be tested after their manufacture, normally at elevated temperatures, which is the burn-in process. The integrated circuits are temporarily installed on a circuit board, tested, and then removed from the circuit board and shipped. Accordingly, test sockets are necessary to install the IC packages on the printed circuit board for testing. These test sockets include multiple contacts to connect each of the terminals of the IC package to corresponding conductors on the printed circuit board. Since the test sockets are used repeatedly in high volume IC package manufacture, it is desirable that the sockets be durable and capable of reliable, repeated operation.
The test sockets are positioned on a burn-in board where the sockets are arranged in a relatively dense array to allow for as many IC packages as possible to be tested at once. These sockets are therefore arranged in a relatively close side-by-side and end-to-end spacing.
It is desirable that the test sockets be capable of conforming to a large tolerance of package thicknesses. IC packages are manufactured with a metal “heat spreader” attached to the back of the package to help more evenly distribute the heat generated by the silicon die that is generally in or on the back of the substrate. A tolerance stack-up builds up because of the thickness tolerances of the IC package, the adhesive joint between the substrate and the “heat spreader,” and the “heat spreader” itself. For example, an IC package can end up with an overall thickness tolerance of + or −0.013 inches.
One of the test socket types that performs the burn-in function includes a base portion and a lid which rotates about one side by way of a hinge, and a latch which holds the lid and base together, where the latch is opposite the hinge. Unless the tolerance of package thickness is accounted for in the design and manufacture of this type of socket, there can be a great disparity in contact pressure between the contacts of the socket and the contact sections of the package. Some prior art examples of this type of test socket are Wells-CTI socket numbers 654, 692 and 693 shown in FIGS. 1–3, respectively.
The prior art Wells-CTI 654 socket 20, shown in FIGS. 1A and 1B, accommodates an IC with length and width dimensions of 8 mm×8 mm. The 654 socket 20 accounts for thickness tolerances by allowing its pressure pad 30 to rock around a center pivot pin 22 mounted parallel to the hinge 24 and by providing compliance via coil springs 26 mounted in its lid 28 on either side of the center pivot pin 22 applying balanced force to the back of the pressure pad 30 and by a coil spring 32 positioned beneath the IC receiver pocket 34.
The prior art Wells-CTI 692 socket 36, shown in FIGS. 2A and 2B, accommodates IC packages with dimensions of approximately 31 mm×31 mm. The 692 socket 36 also accounts for thickness tolerances by allowing its pressure pad 38 to rock around a center pivot pin 40 mounted parallel to the hinge 42. The 692 socket 36 provides compliance by means of coil springs 44 positioned within the corner posts 46 with the lid 48 and latch 50 connected to those corner posts by bars 52 positioned parallel to the hinge 42. The force of the coil springs 44 may be slightly adjusted by adjusting the threaded engagement 54 of the corner posts 46. The adjustment is limited by the properties of the individual coil springs 44 and any wider adjustment would require a complete disassembly of the socket and replacement of the springs.
The prior art Wells-CTI 693 socket 56, shown in FIGS. 3A and 3B, accommodates even larger IC packages 58 with dimensions of up to 42.5 mm×42.5 mm. The 693 socket 56 applies evenly distributed pressure to an IC package 58 via side pads 60 that are linked through symmetrically mechanical rockers 62 to torsional coil springs 64 positioned on the hinge 66 and latch 68 ends of the lid 70. The compliance force of the torsional coil springs 64 can only be adjusted by replacing the torsional coil springs 64, and that requires disassembly of the lid 70.
Therefore, it would be advantageous to have a test socket that accommodates IC packages with a wide range of thickness tolerances by allowing for flexible and more easily adjustable compliance.
The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention which proceeds with reference to the accompanying drawings.